1. Field of the Invention
The present invention relates to an oil pump attachment structure for an engine and more particularly, it relates to an oil pump attachment structure for attaching an oil pump coaxially driven by a crankshaft.
2. Description of the Related Art
As an earlier structure for attaching the oil pump coaxially driven by the crankshaft, there is disclosed an attachment structure where a pump housing is carried inside a front cover for covering a timing chain and disposed between the front cover and a sprocket for a timing chain (Japanese Patent Publication No. 5-059924).
There is also another structure where a pump housing is disposed between the sprocket for the timing chain and a cylinder block, while the pump housing is either projected from the cylinder block for fixture or embedded in a recess formed on a front side of the cylinder block.
However, in case of the attachment structure allowing the front cover to carry the pump housing, the pulsation produced when operating the oil pump directly oscillates the front cover to cause the noise to radiate from the front side of the front cover, so that the engine noise is increased on the front side of the engine disadvantageously.
In case of the structure where the pump housing is disposed between the sprocket for the timing chain and the cylinder block, the running line of the timing chain is apart from the front face of the cylinder block due to the provision of the pump housing. Therefore, the driving force of the timing chain is applied on a camshaft's portion having a large overhang from journals supporting a camshaft while the whole length of the cylinder head is increased. Consequently, there is a possibility of causing the damping performance to be deteriorated due to the reduced rigidity of the camshaft and the journals or causing the weight of the cylinder block to be increased in order to ensure the rigidity of the camshaft and the journals.
In case of the structure where the pump housing is embedded in the front side of the cylinder block, there is produced a problem of causing the cylinder block to be large-sized.